U.S. patent number 5,329,758 [Application Number 08/064,540] was granted by the patent office on 1994-07-19 for steam-augmented gas turbine.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Navy. Invention is credited to Donald T. Knauss, Herman B. Urbach.
United States Patent |
5,329,758 |
Urbach , et al. |
July 19, 1994 |
Steam-augmented gas turbine
Abstract
A steam-augmented gas turbine engine system generally includes a
compressor 3), first and second combustors (4a, 4b), a compressor
turbine (6) and a power turbine (7). A heat exchanging system (8b)
removes heat from an exhaust product from the power turbine (7) and
preheats water which has been desalinated by a water purification
system (12). The desalinated water is provided to the first
combustor (4a), as a predetermined quantity of water-steam mass,
along with fuel and compressed air, and is used to efficiently
power the turbine system. In one embodiment, a two-boiler system
(8b) is employed in which first and second steam outputs are
provided to first and second combustors (4a, 4b) such that a mass
flow of the compressor turbine (6) is substantially constant from a
Cheng point to a stoichiometric point of a predetermined power
profile. This constancy of mass flow ensures that the gas generator
operates on design from the Cheng point to the stoichiometric
combustion point. Additionally, the free-power-turbine (7) always
operates on design.
Inventors: |
Urbach; Herman B. (Annapolis,
MD), Knauss; Donald T. (Severna Park, MD) |
Assignee: |
The United States of America as
represented by the Secretary of the Navy (Washington,
DC)
|
Family
ID: |
22056682 |
Appl.
No.: |
08/064,540 |
Filed: |
May 21, 1993 |
Current U.S.
Class: |
60/775; 60/39.17;
60/39.3; 60/39.55; 60/784 |
Current CPC
Class: |
F01K
21/047 (20130101); F02C 6/003 (20130101) |
Current International
Class: |
F01K
21/04 (20060101); F01K 21/00 (20060101); F02C
6/00 (20060101); F02C 003/30 () |
Field of
Search: |
;60/39.04,39.05,39.07,39.17,39.3,39.53,39.55 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Casaregola; Louis J.
Attorney, Agent or Firm: Miller; Charles D.
Government Interests
STATEMENT OF GOVERNMENT INTEREST
The invention described herein may be manufactured and used by or
for the Government of the United States of America for governmental
purposes without the payment of any royalties thereon or therefor.
Claims
Having thus described our invention, what we claim as new and
desire to secure by Letters Patent is as follows:
1. A steam-augmented engine system, comprising:
compression means for receiving air and discharging a first
compressed air flow mass;
first combustion means for receiving said first compressed air flow
mass, a predetermined quantity of fuel, a predetermined quantity of
purified water and a first predetermined quantity of water and
steam mass, and for generating a first combustion product
therefrom;
heat exchange means for producing said first predetermined quantity
of steam mass and a second predetermined quantity of water and
steam mass;
first expansion means for receiving and expanding said first
combustion product from said first combustion means to generate a
first power output for powering said compression means and for
discharging an expanded combustion product;
second combustion means for receiving said product, a predetermined
quantity of fuel and said second predetermined quantity of water
and steam mass from said heat exchange means, and for generating a
second combustion product therefrom;
second expansion means for receiving and expanding said second
combustion product from said second combustion means to generate a
second power output and for discharging an exhaust product, said
exhaust product being discharged to said heat exchange means;
regulating means for regulating said fuel, said purified water and
said first predetermined and steam mass introduced into said first
combustion means and for regulating said first combustion product,
said fuel and said second predetermined water and steam mass
introduced into said second combustion means, said first and second
combustion means operating along a predetermined power profile,
such that said second combustion means produces a stoichiometric
combustion at a power point; and
sea-water purifying means, coupled to said heat exchange means, for
receiving sea-water, purifying said water and for discharging a
first portion of the purified water to said heat exchange
means.
2. A system according to claim 1, wherein said water purifying
means is coupled to said first combustion means for providing said
purifying water thereto, said purifying water provided to said
first combustion means being a second portion of said purified
water produced by said sea-water purifying means.
3. A system according to claim 1, wherein a mass flow of said first
expansion means is substantially constant from a Cheng point to a
stoichiometric point of said predetermined power profile.
4. A system according to claim 1, wherein total mass flow of
purified water plus steam from the heat exchanger means injected
into said first combustion means is constant.
5. A system according to claim 1, wherein said first predetermined
quantity of water and steam mass has a first characteristic and
said second predetermined quantity of water-steam mass has a second
characteristic.
6. A system according to claim 5, wherein said first and second
characteristics are respective pressures of the first and second
predetermined quantities of water and steam mass.
7. A system according to claim 1, wherein said first predetermined
quantity of water and steam mass has a pressure greater than that
of said second predetermined quantity of water-steam mass.
8. A system according to claim 1, wherein said regulating means
includes means for regulating said second combustion means to
produce a stoichiometric combustion at a predetermined point along
said predetermined power profile, said predetermined point being a
point of maximum power.
9. A system according to claim 1, wherein said heat exchange means
comprises a two-pressure boiler.
10. A system according to claim 1, wherein a stoichiometric
combustion by said second combustion means is based on a
predetermined maximum compressed air flow mass of said compressed
air flow mass, said predetermined maximum compressed air flow mass
comprising a predetermined stoichiometric air flow mass with
respect to said predetermined quantity of fuel.
11. A system according to claim 1, wherein said water purifying
means comprises water desalinating means.
12. A steam-augmented engine system, comprising:
compression means for receiving ambient air and discharging a first
compressed air flow mass;
first combustion means for receiving said first compressed air flow
mass, a predetermined quantity of fuel, a predetermined quantity of
modified water and a first predetermined quantity of water-steam
mass, and for generating a first combustion product therefrom;
heat exchange means for producing said first predetermined quantity
of water-steam mass and a second predetermined quantity of
water-steam mass;
first expansion means for receiving and expanding said first
combustion product from said first combustion means to generate a
first power output for powering said compression means and for
discharging an expanded combustion product as a second power
output;
second combustion means for receiving said second power output, a
predetermined quantity of fuel and said second predetermined
quantity of water-steam mass from said heat exchange means, and for
generating a second combustion product therefrom;
second expansion means for receiving and expanding said second
combustion product from said second combustion means to generate a
third power output and for discharging an exhaust product, said
exhaust product being discharged to said heat exchange means;
regulating means for regulating said compressed air flow mass, said
fuel, said modified water and said first predetermined quantity of
water-steam mass introduced into said first combustion means and
for regulating said second power output, said fuel and said second
predetermined quantity of water-steam mass introduced into said
second combustion means, said first and second combustion means
operating along a predetermined power profile, such that said
second combustion means produces a stoichiometric combustion at a
predetermined point of said predetermined power profile; and
water purifying means for receiving water, modifying said water to
produce said modified water and for discharging a first portion of
the modified water to said heat exchange means,
wherein said water purifying means is coupled to said first
combustion means for providing said modified water thereto, said
modified water provided to said first combustion means being a
second portion of said modified water produced by said water
modifying means,
a mass flow of said first expansion means being substantially
constant from a Cheng point to a stoichiometric point of said
predetermined power profile, said Cheng point being a point of
maximum thermal efficiency.
13. A method of generating power, the method comprising the
following steps:
compressing air to produce a first compressed air flow mass;
modifying water, including desalinating the water to produce a
modified water and discharging a first portion of the modified
water to heat exchange means;
producing a first predetermined quantity of water-steam mass and a
second predetermined quantity of water-steam mass in said heat
exchange means;
providing said first compressed air flow mass to a first combustion
means along with a predetermined quantity of fuel, a predetermined
quantity of said modified water and said first predetermined
quantity of water-steam mass, and generating a first combustion
product therefrom;
expanding said first combustion product and discharging an expanded
combustion product as a first power output;
receiving in a second combustion means said first power output, a
predetermined quantity of fuel and said second predetermined
quantity of water-steam mass from said heat exchange means, and
generating a second combustion product therefrom;
expanding said second combustion product to generate a second power
output and discharging an exhaust product to said heat exchange
means; and
controlling said first compressed air flow mass, said fuel, said
modified water and said first predetermined quantity of water-steam
mass introduced into said first combustion means and regulating
said first power output, said fuel and said second predetermined
water-steam mass introduced into said second combustion means such
that said first and second combustion means operate along a
predetermined power profile and such that said second combustion
means produces a stoichiometric combustion at a predetermined point
of said predetermined power profile, and
wherein a mass flow of the second power output is substantially
constant from a Cheng point to said predetermined point of said
predetermined power profile.
14. A method according to claim 13, wherein said predetermined
point is a stoichiometric point.
15. An engine comprising:
a high pressure combustor;
a low pressure combustor;
a first expansion means operatively connected between the said high
pressure combustor and the said low pressure combustor;
a second expansion means operatively connected to an output of the
said low pressure combustor;
flow sensor and valve means for distributing water and steam and
air to said high pressure combustor and for distributing steam to
said low pressure combustor means so that the mass flow of the
water, steam and air in the high-pressure combustor is held
constant over output power of the engine from the Cheng point to
the stoichiometric point.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to power generation systems
and more particularly to steam-augmented gas turbine engines in
which the compressor turbine mass flow is nearly constant such that
the compressor-turbine performance (isentropic efficiency) remains
on design from a Cheng point to a stoichiometric point.
2. Description of the Related Art
In addition to the usual problems and restrictions associated with
land-installed power plants such as fuel efficiency, cost,
pollution control, and power, shipboard engines have special (i.e.,
stringent) restrictions as to space and weight. Further, the
parameters of fuel efficiency and power are even more important in
naval power plants, where conflicting requirements such as long
patrolling range and high speed may each be achieved, as
required.
To meet the above goals, various engines that have been developed
for land-based power plants have been applied to shipboard power
facilities. One system is a gas turbine based on a simple-cycle
Brayton engine, designated the LM2500 and built by General
Electric. Other engines have also been utilized which have serial
compressors for increasing performance parameters such as power,
fuel efficiency, etc.
Another type of system utilizes steam-augmented gas turbine (SAGT)
engines which are extremely efficient and ecologically-benign.
Commercial versions of this type of engine utilize steam/water flow
rates up to 16% by weight of the airflow rate.
Steam-injected systems generally exhibit higher efficiency and
increased specific horsepower than non-steam-injected systems. Such
systems include many well-known gas turbines produced, for example,
by Allison and General Electric. SAGT engines have been used for
land-based applications in power-producing utilities and in
manufacturing plants that require process steam. However, there has
been only limited interest in shipboard application of the SAGT
concept. The high efficiency of SAGT engines presents many
potential benefits including a decrease in fuel consumption and
extension of ship range and/or the time interval between underway
fuel replenishment. Additionally, SAFT technology offers high
power-turnup ratios for projected pulse-power weapon systems, and
reduced stack weight, vertical moment, and IR signature.
An important concept used frequently in this disclosure is the
Cheng point, described in U.S. Pat. No. 4,297,841, issued to Cheng
and incorporated herein by reference, which corresponds to a SAGT
engine operating at the point of maximum thermal efficiency or peak
efficiency point (i.e., the so-called Cheng point). The Cheng point
occurs approximately when the steam generated by exhaust gases in a
waste-heat boiler becomes saturated.
Another SAGT system is disclosed in U.S. Pat. No. 4,509,324 issued
to Urbach et al. on Apr. 9, 1985, and incorporated herein by
reference. That system is based on a steam-augmented gas-turbine
engine which includes a heat-recovery system (boiler), an
intercooler, and a water-purification system.
FIG. 9 illustrates some basic concepts of SAGT systems wherein a
first compressor 90 receives ambient air at its inlet, compresses
the air and discharges the compressed air to an intercooler 91. The
compressed air is cooled by the intercooler 91, which receives
relatively pure water (i.e., having less than 0.20
parts-per-million solids) at a compatible pressure. The cooled
compressed air is discharged from the intercooler 91 to a second
compressor 92. The output of the second compressor is input to a
combustor 93 and is used to burn fuel in the combustor in the
presence of steam produced by a waste-heat boiler 94 and injected
into the combustor by a steam injection means (not illustrated).
The amount of fuel, steam, and compressed air introduced into the
combustor is regulated in a predetermined manner to ensure
operation of the engine system at a predetermined point (e.g., the
stoichiometric point which is defined as the operating point where
fuel and air are joined in a one-to-one chemical ratio so that all
oxygen is consumed) and along a predetermined power profile curve.
The use of steam in SAGT systems generally yields a specific power
that is approximately threefold greater than the specific power of
simple-cycle engines because a relatively negligible amount of
energy is used to compress water in its liquid state. In the SAGT
engine concept described above, steam/water flow rates up to 50% by
weight of the air flow rate are utilized.
Thus, using up to 50% steam and/or water mixtures increases
gas-turbine engine power by a factor of three or more, while
maintaining the same air flow. Thus, at constant power, the total
air demands are advantageously reduced and hence the size and
number of gas turbine units for a given power requirement may be
reduced accordingly.
The output of the combustor drives the compressor turbine 95, which
drives the first and second compressors 90, 92, and a power turbine
96, which drives a load (not shown). The exhaust from the power
turbine is cooled in the waste-heat boiler 94 which evacuates the
exhaust to a stack and ultimately out to the ambient atmosphere.
The waste thermal energy from the exhaust is used to generate steam
to be input to the combustor. As discussed above, the source of
energy for the injected steam and/or steam-water mixture is waste
heat extracted from the effluent stack gas.
Since, as mentioned above, the energy required to compress the
water is negligible, the available specific power of water is
typically about 1000 hp-sec/lbm as opposed to less than 190
hp-sec/lbm for air in a simple-cycle engine. With maximum
steam/water augmentation, a threefold increase in power output is
achieved without any increment of air flow. At constant power, a
threefold reduction in air requirements is realized. Consequently,
the stack volume of intake and uptake ducts mentioned above can be
substantially reduced in a SAGT engine.
Naval application of SAGT systems demands a large
water-purification system, which had been considered a major
technical impediment to development of a marinized version of the
steam-augmented gas-turbine power plant. However, studies of water
purification based on a reverse-osmosis plant have shown that less
than 4200 cubic feet of space may be required to operate the SAGT
engines for a destroyer with a 100,000-hp propulsion power plant.
Thus, this is not a significant problem.
However, because of the wide range of mass flows necessary in the
SAGT engine, difficulties arise in the previous disclosed engine
from losses incurred by flow regimes which deviate severely from
optimum design-point conditions. As a consequence, although the
overall thermodynamic efficiency is always better than simple-cycle
efficiency, the goal of high efficiency over the entire range of
engine power is not always attained. This is a problem.
Further, the intercooler shown in FIG. 9 helps to increase specific
power and efficiency by increasing the density of air entering the
high-pressure compressor. Therefore, the annular flow area of the
high-pressure compressor must be smaller to match the flow
requirements. Since these changes significantly alter the
characteristics of the new machine, it is very difficult to
manufacture the engine from off-the-shelf components.
Further, while some commercial versions of steam-augmented gas
turbines accept steam in amounts up to 16% of the compressor air
flow, high levels of steam injection are avoided because commercial
turbines, originally designed as simple-cycle machines with smaller
flows, often undergo surge, hazardous overspeed, and serious
off-design losses with greater steam injection.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an
improved, less costly power plant for use on ships as well as
land-based operations.
A second object of the invention is to develop a low-emissions,
affordable, efficient, high-power-density, gas-turbine engine,
which may be produced from off-the-shelf hardware, for shipboard
propulsion, power, and/or other applications.
A third object of the invention is to provide an improved shipboard
engine in which the compressor-turbine power is controlled above
the Cheng point.
A fourth object of the invention is to provide an improved
shipboard engine in which the compressor-turbine mass flow is
nearly constant, such that the turbine performance (isentropic
efficiency) remains on design from a Cheng point to a
stoichiometric point.
A fifth object of the invention is to provide a shipboard engine
which enhances stability and which minimizes fuel consumption
levels at partial loads.
A sixth object is to provide an improved method of generating
power.
One mechanization of the invention has a steam-augmented gas
turbine engine system which includes; compression means for
receiving ambient air and discharging first compressed air flow
mass; first combustion means for receiving the first compressed air
flow mass, a predetermined quantity of fuel, and a first
predetermined quantity of water and steam mass, and for generating
a first combustion product therefrom; heat exchange means for
producing the first predetermined quantity of water and steam mass
and a second predetermined quantity of water and steam mass; first
expansion means for receiving and expanding the first combustion
product from the first combustion means to generate a first power
output for powering the compression means and for discharging an
expanded combustion product, second combustion means for receiving
the above product, a predetermined quantity of fuel and the second
predetermined quantity of water and steam mass from the heat
exchange means, and for generating a second combustion product
therefrom; second expansion means for receiving and expanding the
second combustion product to generate second power output for
powering a load coupled to the second expansion means and for
discharging an exhaust product, the exhaust product being
discharged to the heat exchange means; regulating means for
regulating the fuel, and the first predetermined water and steam
mass introduced into the first combustion means, and the fuel and
the second predetermined water and steam mass introduced into the
second combustion means such that the second combustion means
produces a stoichiometric combustion at a power point of a
predetermined power profile curve; and purification means, coupled
to the heat exchange means, for receiving seawater, purifying the
seawater, and discharging a first portion of the purified water to
the heat exchange means, wherein the first steam receiving means is
coupled to the first combustion means for providing the steam
thereto, and wherein a second water and steam receiving means is
coupled to a second combustion means for providing water and steam
thereto; and in, conjunction with the steam to the first receiving
means, a second portion of purified water is discharged directly to
the first combustion means, such that the mass flow of the first
expansion means is substantially constant from the Cheng point to
the stoichiometric point of the predetermined power profile.
With the invention, an improved, less costly power plant for use on
ships as well as land-based operations is provided. Further, the
invention provides an improved shipboard engine in which the
compressor-turbine power is controlled above the Cheng point and in
which compressor-turbinemass flow is nearly constant, such that the
turbine performance(isentropic efficiency) remains on design from a
Cheng point to a stoichiometric point. Additionally, the invention
provides a shipboard engine which enhances stability and which
minimizes fuel consumption levels at partial loads.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, aspects and advantages will be
better understood from the following detailed description of a
preferred embodiment of the invention with reference to the
drawings, in which:
FIG. 1 is a schematic of a general embodiment of the invention
including engine cooling and steam generation flow circuits;
FIG. 2 illustrates a heat recovery steam generator (HRSG) with a
recirculating boiler which is a portion of the SAGT engine shown in
FIG. 1;
FIG. 3 is a schematic of another embodiment of the present
invention illustrating a reheat steam-augmented gas turbine (SAGT)
engine with a two-pressure boiler;
FIG. 4 illustrates the SAGT turbine flow regimes;
FIG. 5 illustrates a relationship between the overall thermodynamic
efficiency versus specific power for a SAGT engine having an
intercooler;
FIG. 6 illustrates comparative fuel consumption characteristics
between the present invention and conventional engines;
FIG. 7 illustrates specific fuel consumption characteristics versus
ship speed, for the present invention as compared to the
conventional engines;
FIGS. 8(a) and 8(b) illustrate a layout of the SAGT plant in the
aft portside engine room in a vessel, with FIG. 8(a) being a plan
view of the second platform and FIG. 8(b) illustrating an overall
side elevation view; and
FIG. 9 is a schematic of a conventional SAGT engine having an
intercooler.
FIG. 10 is a schematic diagram of one possible flow control scheme
for the FIG. 3 device.
Referring now to the drawings, and more particularly to FIG. 1,
there is shown a schematic diagram of a general embodiment of a
SAGT engine according to the invention which includes first and
second compressors, a cooler, a compressor turbine, a power turbine
and a heat exchanging system, which includes a heat recovery steam
generating system and feedwater and seawater heating mechanisms, a
water purification system, and a seawater storage unit.
As shown in FIG. 1, a first compressor 1 receives ambient air at
its input, compresses the air and discharges the compressed air to
an intercooler 2. The compressed air is cooled by the intercooler
and is output to the second compressor 3. The second compressor
compresses the cooled compressed air received from the intercooler
2.
The second compressor discharges the compressed air to a combustor
4, where it is used to burn fuel in the combustor in the presence
of steam injected by a steam injection device 5 which may include a
valve or the like.
A regulator 5', which may include a plurality of valves and sensing
means, regulates the amount of fuel, steam and compressed air
introduced into the combustor in a predetermined manner to ensure
operation of the engine system at a predetermined point (e.g., the
stoichiometric point discussed in more detail below) along a
predetermined power profile curve. The output of the combustor is
used to drive a compressor turbine 6, which drives the first and
second compressors and a power turbine 7 and which drives a load
(not shown) by expanding the combustion product from the combustor
4.
The exhaust from the power turbine 7 is output to a heat recovery
steam generator (HRSG) 8. The steam generator 8 cools the exhaust
from the turbine 7 and discharges the exhaust to the stack and
ultimately out to the ambient atmosphere. The steam generator
generates steam to be input to the combustor 4 via valve 5. The
heat recovery steam generator is preferably a water tube boiler
having a forced recirculation loop to maintain acceptable water
quality within the evaporator. The steam generator forms part of
the heat exchanging unit discussed in further detail below.
Suitable control means controls system operation.
Simultaneously with the operation of the structure described above,
a pump 9 circulates water from a seawater heater 10 to the
intercooler 2 in a countercurrent flow arrangement with respect to
the compressed air being output from the first compressor to the
second compressor via the intercooler. Heat is extracted from the
compressed air being generated by the first compressor 1. Much of
the heat extracted from the compressed air generated in the
compressor 1 is transferred to the boiler feedwater in a feedwater
heater (FWH) 11.
Additional energy is extracted from the intercooler stream in the
seawater heater (SWH) 10, which warms the seawater prior to entry
into a reverse osmosis desalinator (ROD) 12. Seawater, optimally
warmed to approximately 90 degrees F., is pumped by a pump 13 from
a sea chest (seawater storage means) 14 through the seawater heater
10 to the reverse osmosis desalinator 12.
The reverse osmosis desalinator purifies and desalinates the
seawater to a level of preferably 200 parts per billion (ppb) of
total dissolved solid since extremely high purity steam is required
for injection into gas turbines. If this quality is not obtained,
wash-down frequency must increase inordinately or serious damage
may occur to the gas turbine. The water treatment system must also
be designed to minimize power consumption. Water treatment systems
other than distillation systems may be used to produce the high
purity water for steam injection, including (1) membrane
distillation (MD), (2) two-pass reverse osmosis (RO), (3) two-pass
RO followed by continuous deionization and (4) a three-pass RO.
Water from the sea chest 14 is also pumped by pump 13 to a control
condenser 15 via a valve 16. The condenser 15 functions to evacuate
steam not used by the combustor and quickly condenses steam to
purge it from the system during emergency engine shutdowns.
Seawater cools the steam preferably by direct contact. The control
condenser 15 is coupled to the output from the steam generator via
regulating means 27, as shown in FIG. 1, and an output from the
seawater chest 14 via regulating means 16. A predetermined
water/steam mass is provided from the steam generator to the
combustor via regulating means 5.
Purified water from the ROD 12 is pumped by a pump 17 to a
plurality of feedwater (FW) tanks 18 or the feedwater heater 11. A
pump 19 delivers the purified water from the feedwater heater at
pressure to the heat-recovery steam generator 8. The steam
generator 8 includes a recirculating pump 8a for preventing fouling
of the boiler by ensuring that the heat-exchanger surfaces are
never dry.
A pump 20 in line with the plurality of tanks 18 provides
additional purified water to the steam generator 8, via the
feedwater heater 11, as required. As mentioned above, the steam
generator generates steam which is returned to the combustor to
provide power to the compressors, compressor turbine and power
turbine.
Warmed rejected brine from the reverse osmosis desalinator 12 may
be rejected to the sea and/or may be passed, via a valve 21 and
pump 22, through the seawater heater to extract heat, depending
upon the ambient water temperature. For example, if the ambient
water temperature is less than 85 degrees F., then it may be
advantageous to extract heat therefrom by passing it through the
seawater heater 10. Further, seawater may be rejected, as required,
via a valve 23 in line between the input of the ROD and the output
of the seawater heater.
The intercooler 2 is preferably a plate/fin type exchanger, and the
SWH and the FWH preferably are a plate/frame type. All units
preferably employ a counterflow arrangement to ensure maximum
efficiency of thermal energy transfer.
Various regulating means, sensing means and monitors may be
suitably employed with the above-mentioned structure to ensure
maximum efficiency and output of the system. For example, a
regulating means 24 and valve 25 is employed in line between an
output of the intercooler and an input of the feedwater heater to
transfer heat from the heated water from the intercooler to the
feedwater heater and the water being provided to the heat recovery
steam generator. The regulating means also is positioned in line
between the inlet of the feedwater heater 11 and the output of the
seawater heater 10 to regulate flow of seawater from the heater 10
to the feedwater heater 11.
A second regulating means 26 may be advantageously employed in line
between the output of the feedwater tank and an input of the
feedwater heater. The second regulating means 26 may also be
employed in line between the output of the ROD 12 and the input of
the feedwater heater, as shown in FIG. 1.
As mentioned above, other regulating means are preferably employed
to regulate the amount of fuel, and water and steam mass from the
steam generator 8, in accordance with predetermined maps or the
like to achieve maximum efficiency along a predetermined power
profile.
Looking at the system in greater detail and specifically the heat
exchanging system, to maximize the thermal efficiency of the
overall plant, illustrated in the schematic of FIG. 1, thermal
energy from the intercooler 2 is utilized by the seawater heater 10
which heats seawater for the reverse osmosis desalinator 12, and by
the feedwater heater 11, which serves the heat-recovery steam
generator 8. Any residual energy/heated water not utilized in the
ROD is dumped overboard with seawater discharge. Further, a valve
23 may be installed in line between the output of the seawater
heater and the ROD to evacuate seawater therefrom, as required.
During operation of the SAGT engine at stoichiometric conditions or
at low-ambient temperature, seawater heating can be augmented by
diverting warm brine from the ROD through the SWH via a valve
31.
An important consideration in sizing the heat exchanger within the
purview of those skilled in the art and in light of the present
disclosure of FIG. 1 is to maintain, under operating conditions, an
ROD seawater inlet temperature of preferably approximately
90.degree. F., while maximizing the heating of the heat recovery
steam generator feedwater. This must be done over a broad range of
steam rates (i.e., the Cheng point, discussed in further detail
below, to the stoichiometric point) and at all ambient
temperatures.
While the design points for the intercooler, FWH and HRSG are
governed only by stoichiometric operation at 100.degree. F. ambient
temperature, the design of the seawater heater is governed by three
different operating conditions. For example, design of the seawater
heater considers (1) high ambient temperature under loss of water
(ROD shutdown), (2) low ambient temperature with water production,
and (3) high-ambient temperature, with Cheng-point operation, where
relatively high heat loads, combined with ROD inlet temperature
constraints, demand much higher seawater flows than those
encountered at any other operating conditions.
FIG. 2 shows a general embodiment of the heat recovery steam
generator 8 in which a desuperheater 83 is employed because of the
extremely broad range of steam flows demanded by the plant; e.g.,
between the Cheng point and stoichiometric point, the water flow
increases by a factor of about 2.5.
In FIG. 2, a steam drum 81, which collects saturated steam, is
coupled to a superheater 82 for generating dry steam and which in
turn is coupled to a desuperheater 83. Blow-down of water is
performed to evacuate excess water and solid contaminants (i.e.,
salt) from the steam drum. The desuperheater 83 mixes cold water
and superheated steam to condense the steam. Another output of the
steam drum is coupled to a recirculating pump 84 which in turn is
coupled to a boiler 85 which heats the water input by pump 84.
Boiler 85 provides the steam/water product to the steam drum. An
economizer 86 is provided for receiving water from an external unit
(i.e., the feedwater heater or directly from the ROD unit, not
shown in FIG. 2) and for delivering an input to the steam drum and
to the desuperheater 83 via a regulating means (i.e., valve 87) or
the like.
The weights and volumes of the various heat exchanging units for a
100,000-hp plant are presented below in Table 1.
TABLE 1 ______________________________________ WEIGHTS AND VOLUMES
OF VARIOUS HEAT EXCHANGER MEMBERS. WET WEIGHT VOLUME (LBS)
(FT.sup.3) ______________________________________ INCLR 3915 89 SWH
7049 124 FWH 2510 60 HRSG CORE 42688 674 NOZZLE & DIFFUSER 6592
1720 STEAM DRUM 13440 306 DESUPERHEATER & 4480 140 CONDENSER
TOTAL 80674 3113 ______________________________________
At initiation of injection, the water is highly superheated but
below the turbine inlet temperature (TIT). Since, for nominal
increases in water flow, little additional fuel is required to
maintain the TIT at the desired value, the thermal efficiency
increases rapidly. The peak efficiency point (i.e., the Cheng
point) occurs approximately where the steam becomes saturated. As
more water is introduced, the specific enthalpy of the steam and/or
the steam-water mixture drops off. Increasing the amounts of
injected steam and/or steam and water mixture requires more fuel to
maintain the TIT. Thus, beyond the Cheng point, the overall thermal
efficiency falls monotonically to the stoichiometric-point value,
which may be above comparable simple-cycle efficiencies.
The most likely ship-power demand corresponds to an engine power
level in the vicinity of the Cheng point. The maximum specific
power of SAGT engines is approximately threefold greater than the
specific power of simple-cycle engines. Thus, at constant power,
the total air demands may be reduced threefold. Since the airflow
of a gas turbine is a measure of its overall cost, the size and
number of gas turbine units for a given power requirement may be
reduced. Additionally, because boiler and water purification
systems are not as expensive as gas turbines, there may be a modest
cost reduction over systems employing simple-cycle engines.
Regarding engine sizing for a chosen propulsion system, a choice of
four, rather than two, engines in the destroyer application
provides a redundancy that addresses the Navy need for
survivability, and also allows for more efficient energy
consumption. However, the choice of two engines, employed herein
for the SAGT engine, simplifies design and construction, and
provides a reduction of initial costs.
The high specific power of steam (1000 hp-sec/lbm mentioned above)
produces, in the SAGT engine at the stoichiometric point, a
specific power of about 590 hp-sec/lbm of working fluid in the
compressor. The specific power of an LM2500 engine, commercially
available from the General Electric Corporation and the standard
propulsion engine for destroyers, is 187 hp-sec/lbm. Thus, the
specific power of the working fluid in the SAGT engine is about
three times greater than that of the LM2500 engine (i.e., a 3.1:1
ratio). Thus, the power generation by the SAGT engine is much
higher than that of the conventional LM2500 engine.
One LM2500 engine delivers 25,000 hp in the simple-cycle mode,
whereas a SAGT engine operating at the stoichiometric point,
delivers only 16,100 hp in the simple-cycle mode. However, with
injection of steam, the factor of 3.1:1 increases the power output
of the SAGT engine to 50,000 hp. Thus, only two SAGT engines
operating at stoichiometric conditions are required to yield
100,000 hp normally supplied by four LM2500 engines.
Air consumption may be estimated by proportioning the air flow and
power ratios of off-the-shelf commercial engines. The proportioning
leads to an air flow of 94.3 lbm/sec for one engine at 59 degrees
F. ambient temperature, which, for a 100-degree F. day, corresponds
to 87.4 lbm/sec, or 175 lbm/sec for two engines. This
air-consumption rate and power suggest that the air consumption of
the SAGT compressor is similar to the air consumption of a
conventional LM1600 gas turbine.
The injection of large quantities of steam into the combustor
requires an increase in the cross-sectional areas of the combustor
and the subsequent turbine stages to accommodate the increased
volume of flow. If the cross-sectional areas of the combustor and
the turbine stages were not increased, problems relating to
choking, overspeed, vibration and destruction would arise. The
stoichiometric quantity of water needed for a gas turbine varies
with the particular cycle character, such as the bleed rates and
the maximum allowable combustion temperature. For example, within
the purview of those skilled in the art, for a TIT of 2200 degrees
F., the percentage of water (i.e., with respect to air) injected
into the combustor will be about 47.5%. With provision for a 5%
steam bleed for cooling, the total water demand with respect to air
may exceed 52.5%. A 2% overboard bleed air rate (1.8 lbm/sec) for
cooling is diverted from the turbines and dumped into the stack.
Data for the mass flow rates at stoichiometric conditions,
including fuel and steam, are listed in Table 2 below.
TABLE 2 ______________________________________ ANTICIPATED MASS
FLOWS FOR SELECTED FLOW STATIONS IN A 50,000-HP SAGT ENGINE. MASS
FLOW RATE FLOW STATION (LB/SEC/UNIT)
______________________________________ Compressor Inlet 87.4
Overboard Air 1.8 Bleed High Pressure 133.0 Turbine Inlet Gas-side
Boiler 139.0 Inlet Water-side Boiler 45.1 Inlet
______________________________________
The turbine flow matches the inlet flow for an LM2500 engine.
Further, water consumption at the Cheng point is about 40% of the
consumption rate at the stoichiometric point (coolant steam is
included in this calculation). Water-production rates corresponding
to full-throttle or near full-throttle power are required for only
a small percentage of overall operating time. Indeed, studies have
shown that the time needed for speeds exceeding 27 knots is only 6%
of the total time (but 15% of the total fuel consumption). For some
ships underway at cruise speeds or less, it would be impossible to
store (in the fuel tanks) all the water produced by a water plant
sized for stoichiometric consumption.
With steam and/or water injection as a standard operating procedure
over the entire range of power, the low-end range of compressor
mass-flow rates and power is expanded. The additional flow of steam
in the turbines stabilizes operation of the compressors at lower
mass flows, where they are subject to stall. However, at high mass
flows, where high power is demanded, choking, vibration and
overspeed (i.e., of the turbine blades) are problems as mentioned
above.
For highest fuel efficiency, the SAGT gas turbine of the invention
is designed so that the ship cruise condition is in the
neighborhood of the Cheng point. SAGT turbines attain peak
permissible pressure ratios and TIT near the Cheng point, where
compressor flow is maximum. Between the Cheng point and the
stoichiometric point, the compressor section is expected to operate
at a fixed speed compatible with the maximum air flow rate and
TIT.
With increased steam injection above the Cheng point, the
compressor turbine must accept, without choking, as much as 30%
additional mass flow having 10% greater specific volume, with the
potential to do about 45% more work. Choking flow is preferably
avoided by increased pressure and/or lower temperature, reduced
consumption of air, expanded annular areas, or bleeding of the
working fluid through some bypass to downstream stages.
Another embodiment of the invention is illustrated in FIG. 3, in
which like elements shown in the embodiment of FIG. 1 are shown by
like numerals. With this embodiment, compressor-turbine mass flow
above the Cheng point is nearly constant, such that the turbine
performance (isentropic efficiency) remains on design from the
Cheng point to a stoichiometric point.
Generally, the embodiment of FIG. 3 utilizes many of the same
elements as that of FIG. 1. However, it dispenses with the
intercooler, and (See the system of FIG. 3) incorporates a
low-pressure combustor 4b, which provides some reheat prior to the
free-power turbine 7. A two-pressure, recirculating, waste-heat
boiler 8b provides steam to the combustors. A reverse-osmosis
desalination water treatment system 12 generates highly purified
water for the boiler(s). In the absence of water, SAGT power
production may continue at reduced power.
The two-pressure boiler system 8b of FIG. 3 provides for proper
distribution of steam flow into the combustors. This two-pressure
boiler system addresses the problems associated with stoichiometric
operation, such as compressor overspeed and off-design losses. The
two-pressure SAGT of FIG. 3 permits the flow regimes to be
controlled in a manner which maintains the system close to design
conditions and high efficiency.
Looking at the SAGT engine illustrated in FIG. 3 in greater detail,
low-pressure steam is routed at matching pressure, through a
conventional lossy throttle, directly to a low-pressure combustor
4b upstream of the power turbine 7. The design point mass flow in
combustor 4b is about 25% water (i.e., not the Cheng point). The
inlet temperature to the turbine is held substantially constant
even with maximum fuel flow at the stoichiometric point, by
decreasing steam quality. Reheating of the working fluid prior to
entry into the free power turbine 7 increases efficiency of the
system. System operation is controlled by suitable control means,
and the fuel, water and steam masses input to the first and second
combustion chambers are regulated by suitable regulating means
indicated generally by item 5".
FIG. 10 is a diagram illustrating schematically one method of
controlling the flow of fuel, water and steam to the combustors of
the FIG. 3 embodiment of the invention. The controller, item 1000
can be comprised of any conventional means which will sense the
levels of the signals arriving from the various flow meters or
sensors and will send out signals to actuate the various flow
control valves in response to detection of particular levels of the
sensed signals. The controller function can be mechanized using
conventional electrical, electromechanical or electrohydraulic
components or alternatively by a suitably programmed
microprocessor. The particular levels to be detected will depend
upon the specific design of a particular machine. Other schemes to
control flow will be obvious to those of skill in the art. For
instance simple detectors (electrical, electromechanical or
electrohydraulic) can be used to sense the flows and actuate the
valves directly.
It is important to consume as much fuel as possible in the
high-pressure combustor to achieve high specific power. If
insufficient fuel is burned in the high-pressure combustor, the
burden of attaining stoichiometry is shifted to the low-pressure
combustor. Thus, the elevation of temperatures in the
free-power-turbine and the boiler may exceed levels compatible with
the material integrity of these components. The contrivance of
using cold water in conjunction with sufficient fuel to attain
stoichiometry is clarified by reference to FIG. 4.
A gradual diversion of the steam flow, away from the high-pressure
combustor to the low-pressure combustor, is contrived to avoid a
wide variation in mass flows, and efficiency remains high. As shown
in FIG. 4, the steam flow to the high-pressure compressor is
replaced, pound for pound, with equal amounts of cold water. Thus,
the mass flow in the gas generator(compressor and
compressor-turbine) is nearly constant, except for addition of
fuel, over a wide range of power output (from about 35% to 100% of
power in FIG. 4). The scheme permits consumption of most of the
fuel and oxygen in the high-pressure combustor.
At power levels below 35%, the gas generator is stabilized by the
steam flow injected into the turbine. Therefore, the gas generator
remains close to the design point operation most of the time. Since
the free-power turbine may accelerate freely with mass flow, the
free power turbine is on design all the time. The partial reheat
capability of the new SAGT engine is available for operation during
any flow regime.
The gas-turbine engine of the FIG. 3 embodiment includes provisions
for reheat and design-point operation over a wide range of power up
to the stoichiometric combustion point.
The design point in FIG. 4 is the point where fuel addition to the
low pressure combustor must begin in order to achieve full-power
stoichiometric operation. However, fuel addition may begin sooner
to take advantage of the promise of the higher efficiency provided
by reheat. The free-power turbine mass flow, indicated by the
dotted line, becomes identical with the gas-generator flow below
the Cheng point.
Thus, FIG. 4 illustrates that at the Cheng point, steam is diverted
from the high-pressure combustor 4a to the low-pressure combustor
4b. However, the turbine mass flow (see the solid curve) is nearly
constant, except for small additions of fuel, because water is
injected into the high-pressure combustor 4a in amounts precisely
equal to the diverted steam.
Thus, with the structure of the invention, the gas generator
achieves its design objectives, with respect to mass flow, from the
Cheng point to the stoichiometric point. Specifically, as clearly
shown in FIG. 4, the fluid flow rate of the compressor turbine from
the Cheng point to the stoichiometric point is substantially
constant, with the free power turbine 7 remaining on its
theoretical performance profile (i.e., its design) so long as speed
of the turbine drive shaft is proportional to the axial
working-fluid velocity. Further, the free power turbine 7 utilizes
blades which have a constant shape and are at a fixed optimum
orientation. Thus, no adjustable inlet vane blades are required by
the free power turbine of the invention.
More importantly, the two-pressure boiler 8a eliminates the need
for design of a hot-end bypass valve, cooled manifolding for
bypassed flow, and cooled blades in the first stage of the power
turbine. With the two-pressure boiler, combining components from
the existing gas-turbine components may be performed to achieve the
desired machine, and indeed such is contemplated by the present
inventors. Since the new SAGT engine dispenses with an intercooler,
assembly of the engine is contrived largely from off-the-shelf
hardware. Thus, excluding development costs, the engine is expected
to be cost-wise competitive with the baseline engine. Further,
compressor-turbine power is controlled above the Cheng point and
compressor-turbine mass flow is nearly constant, such that the
turbine has constant performance from the Cheng point to the
stoichiometric point.
To validate the inventors' findings, the performance of the SAGT
systems was computed using real-gas data with a point-design
program and a map-matching program. The two programs offered a
cross-check on their consistency with respect to first and
second-law thermodynamic checks. Most of the data were based upon
the conventional internal bypass concept which diverts excess
working fluid around the compressor-turbine. Data on efficiency are
expected to be higher with the reheat SAGT concept shown in FIG.
3.
The prediction of performance was aimed at the previously discussed
50,000-horsepower steam-augmented gas turbine for a destroyer
(i.e., a DDG 51 class vessel) with two power plants, rather than
the customary four. The performance prediction program was written
to accept a wide range of variables and could be extended to almost
any reasonable range for a SAGT design. Some design parameters and
inputs are listed in Table 3.
TABLE 3 ______________________________________ Principle design
input data ______________________________________ Maximum Turbine
Inlet 2200 F. Temperature Maximum Pressure Ratio 16 Minimum WHB
Exhaust 450 F. Temperature Ambient Temperature 100 F. Seawater
Temperature 85 F. Lower Fuel Heating 18,300 Value BTU/lbm Maximum
Compressor 0.86 Efficiency Maximum Turbine 0.90 to 0.92
Efficiencies Burner and Gas 0.995 Generator Efficiency Pressure
Loss Ratio Burner 0.035 Intercooler 0.02 Intercooler Effectiveness
0.88 Stoichiometric Point 0.735 Cheng Point Stoichiometric Fuel-Air
0.0658 Ratio ______________________________________
Location of the Cheng point varies, depending primarily on design
conditions, component efficiencies, water-air ratios, and general
limitations. The design point is preferably chosen to distribute
fuel consumption between the combustors in a manner which optimizes
performance and is compatible with material temperature limits.
Slightly superheated steam is used in place of compressor bleed air
for blade cooling purposes. Since steam has twice the specific heat
of air, the mass flow is only about half that required for
comparable air cooling. In computer calculations, a steam-cooling
bleed flow and a compressor air bleed flow of 0.035 and 0.02 pounds
per pound of inlet air per second, respectively, are used. Half of
the air bleed was considered lost as overboard bleed while the
remaining bleed air and all the steam bleed were recombined with
the main flow, for calculational purposes, between the compressor
turbine and the power turbine.
FIG. 5 illustrates the performance of the steam injected gas
turbine over its power range for the basic inputs of Table 3.
Overall thermal efficiency is plotted versus specific power, where
specific power represents how much output horsepower can be
obtained per pound of inlet air per unit time.
As a basis for comparison, the aforementioned specific power of the
present marinized LM2500, 187 hp-sec/lbm, with a thermal efficiency
of 36 percent, is shown as a single point in FIG. 5. The SAGT
turbine has specific powers of 350 and 588 hp-sec/lbm of inlet air
and thermal efficiencies of 42.8 and 35.2 percent at the Cheng and
stoichiometric points, respectively. Selected data from a
simulation program are included in FIG. 5, with corrections for
losses from operation of the reverse-osmosis water plant.
The high specific power of the SAGT engine permits a single SAGT
turbine to replace a pair of LM2500 engines and produce the same
maximum power with only about one-third of the stack requirement.
The peak efficiency region around the Cheng point falls in the
mid-power range, which represents the majority of ship operational
life.
Turning to the main reduction gear for the SAGT engine, the engine
room on the DDG-51 class destroyer is currently equipped with two
LM2500 gas turbines, a dual-input, single-output, locked-train,
double reduction (LTDR) main reduction gear (MRG) and supporting
equipment for a controllable/reversible pitch (CRP) propeller. Even
with one turbine eliminated, engine-room changes may be kept to a
minimum since the 50,000-hp SAGT engine will have approximately the
same footprint as a 25,000-hp LM2500. Preferably, the SAGT engine
is placed on the existing foundation for the inboard LM2500 and the
center distance from the turbine shaft to the propeller shaft
remains unchanged. Also, for strict comparability with the existing
DDG-51, a controllable/reversible pitch propeller is assumed. No
modification to the 50,000 hp DDG-51 CRP is required.
A single-input, single-output, locked-train, double-reduction gear
similar to one branch of the DDG-51 MRG is preferably used. This
would allow the turbine shaft and propeller shaft centers to be
maintained and would provide access to the center of the propeller
shaft at the forward end, which is needed to mount the oil
distribution box for control of the CRP.
Direct comparability is maintained by continuing to use a K factor
(a measure of surface hardness) of 350 for the conceptual gear
design. The length-to-diameter (l/d) ratio of the pinions is
allowed to go as high as 2.1, provided that helix angle corrections
are made on the teeth. This restriction is due to pinion bending
when loaded and is not likely to be increased. While there is some
margin to both limits in the first reduction of the DDG-51 MRG,
both K factor and l/d ratio are near their limits in the second
reduction. Major design parameters, and final weight and volume
data for the single input 50,000-hp LTDR gear are shown in Table
4.
TABLE 4 ______________________________________ Locked train double
reduction gear parameters for use with 50,000-hp SAGT turbine and
CRP. First Second Reduction Reduction
______________________________________ K-Factor 350 350 Pinion
Speed, rpm 3600 1100 Gear Speed, rpm 1100 168 Pinion Pitch Dia.,
13.96 17.21 (in.) Gear Pitch Diameter 45.69 112.70 (in.) Face
Width, (in.) 16.75 31.84 Center Distance, 29.82 64.96 (in.) Pinion
1/d Ratio 1.49 2.08 (incl. 4" gap) Weight, lbs, total 124,700
Volume, cu. ft., total 445,500
______________________________________
The substantially lower air flow and the increased density of the
stack effluent gases permit a large reduction in stack system
volume. Tables 5 and 6 detail the calculations estimated to
determine the stack volume and weight of the SAGT system.
Dimensional data for the SAGT system in Table 6 are not given since
there is no extant hardware. The areas were computed from an
analysis of the mass flows and the effects of molecular weight and
temperature on the density of the effluent gases. Volumes of the
stacks were based upon the computed areas and the stack heights of
the baseline propulsion power plant. The weight of the SAGT stack
system was obtained by assuming a linear proportionality between
the weight and volume.
TABLE 5 ______________________________________ Stack system data
for LM2500 systems ______________________________________ Intake
mass flow for 133.3 lb/sec one engine Secondary cooling flow 26.5
Total flow at the 159.8 intake Uptake flow for the 135.7 engine
Untake flow plus 162.5 cooling flow Intake 8.25 ft. length 7.73 ft.
width 53.0 ft. height 63.8 ft.sup.2 area 3381 ft.sup.3 volume
Uptake 7.63 ft. length 5.0 ft. width 63.0 ft. height 38.2 ft.sup.2
area 2407 ft.sup.3 volume Stack volume per 5788 engine Stack volume
for four 23152 units Estimated stack 3450 spacing volume Total
stack system 26500 ft.sup.3 volume Total SWBS stack 176.6 t system
weight including casing ______________________________________
TABLE 6 ______________________________________ Stack system data
for a SAGT system ______________________________________ Intake
mass flow for one 87.4 lb/sec engine Secondary cooling flow 26.5
Total flow at the intake 113.9 Uptake flow for the 139.0 engine
Uptake flow plus cooling 165.5 flow Intake 53.0 ft. height 46.9
ft.sup.2 area 1709 ft.sup.3 volume Uptake 63.0 ft. height 27.1
ft.sup.2 area 2486 ft.sup.3 volume Stack volume per engine 4195
Stack volume for two 8390 units Estimated stack system 1740 spacing
Total stack system volume 10130 ft.sup.3 Total SAGT system stack
60.7 t weight by proportion
______________________________________
An alternative propulsion plant which may be employed is the
intercooled regenerative (ICR) gas turbine power plant. The intake
and uptake flow areas were based upon employing 3.79 ICR engines
since the power output of an ICR engine is 5.5% greater than the
power output of an LM2500 engine. Also, the lower temperature in
the effluent gas of the output increases the gas density and
reduces the overall uptake stack size. The computed data for the
volume and weight of the ICR plant are 23170 ft3 and 135.7 t,
respectively.
Application of the invention to an existing gas turbine, such as
the propulsion plant of a DDG-51, and the feasibility thereof must
include examination of the system fuel consumption. The typical
engine performance data of FIG. 6 show the specific fuel
consumptions as a function of percent total output of the three
engine types, i.e., the baseline LM2500, the ICR, and the SAGT
engine of FIG. 1.
Assuming that each of the engine types of FIG. 6 is of the same
output power, the solid curve corresponds to the LM2500, which
requires more fuel for any output power. The calculated SAGT data,
points represented by circles, indicate that the SAGT system (of
FIG. 1) may not be as efficient as the ICR system (with calculated
points represented by diamonds) at high-power conditions. However,
the SAGT engine with the reheat combustor of FIG. 3 would be more
efficient than the ICR engine because reheat makes the engine
approach Carnot-cycle efficiency.
The specific fuel consumption can be analyzed from the data in FIG.
6 and the ship's power profile, to obtain a plot of specific fuel
consumption versus ship speed in knots, as shown in FIG. 7. The
curve corresponding to the squares and solid line yields the
specific fuel consumption for a destroyer (i.e., a DDG 51) with
four LM2500 engines. The open circles represent the specific fuel
consumption of a two-engine SAGT propulsion plant. The triangles
represent a four-engine ICR propulsion plant. As shown in FIG. 6,
as the fuel consumption increases, the output power percentage
decreases, with the SAGT having roughly the same fuel consumption
as the LM2500 at 100% output power.
Table 7 presents the required fuel tonnage for the alternate
systems based on the same power profile. For this particular power
profile, the fuel requirement for the SAGT power plants for one
year is 8292 metric tons. Similar analyses made for the ICR and the
baseline LM2500 power plants are shown. The percentage fuel savings
obtained by the two-engine SAGT plant, 21.5%, approaches the listed
23.1% savings of the four-engine ICR plant. Fuel consumption of
SAGT power plants employing the low pressure reheat combustor is
less than that of the ICR power plant.
TABLE 7 ______________________________________ Comparison of fuel
consumption for selected alternative DDG-51 propulsion plants. Ship
propulsion plant Fuel tons/year Savings %
______________________________________ Four-engine LM2500 10560 --
Four-engine ICR 8120 23.1 Two-engine SAGT 8292 21.5
______________________________________
Turning to the sizing of the propulsion plant, with the weight and
volume data of the baseline LM2500 reference plant on the DDG-51
known and with all components of the propulsion plant assumed to be
rectangularly-shaped in the computation of volumes, a comparison of
such data with analogous weights and volumes of the propulsion
components for the ICR power plants has been made. Since the power
output of the ICR engines is larger (26500 hp) only 3.79 units were
weighed into the final weight tally of Table 9.
In the data of Table 8, there is a separate accounting of
propulsion weight supports (at a very conservative 30% of the
primary weight) for such components as boilers and
regenerators.
TABLE 8 ______________________________________ SAGT system sizes
and weight. VOLUME, COMPONENT ft.sup.3 (m.sup.3) WEIGHT, lbm (l.t.)
______________________________________ Gas turbine package 3,830
(108.5) 97,000 (44.0)a Propulsion Foundations 348 (9.8) 86,913
(39.4) Stack system 10,130 (286.8) 132,875 (60.3) Boiler (wet)
4,175 (118.2)b 133,740 (60.7)c Boiler Foundation 160 (4.5) 40,123
(18.2) Intercooler/SWH/FWH 641 (18.2) 26,950 (12.2) (wet) Reduction
Gear 3,630 (102.7) 248,000 (112.5) Water Plant 3,822 (108.2)
147,400 (66.9) Pumps and Motors 138 (3.9) 12,320 (5.6) Total System
26,874 (761) 925,320 (419.8) ______________________________________
a) Based upon two LM2500 engines. b) Assumed density is 250
lbm/ft3. c) 30% of the boiler weight.
It is assumed that with a mass flow of 87 lbm/sec, the front end of
the SAGT engine will be smaller than the front end of an LM1600.
The hot-section compressor turbine will require a throughput mass
flow of about 105 lbm/sec and thus, should be somewhat smaller than
an LM2500 hot-section turbine. Finally, the free power turbine will
handle a throughput of about 131 lbm/sec., which is close to design
for the LM2500. Thus, the turbine weight of the SAGT engine is
assumed to be that of a boxed Navy LM2500 engine.
Boiler weights and sizes (see above section) were investigated
against existing hardware to assure accuracy of data. SAGT weights
for the heat exchanger were wet weights, whereas the listed
intercooler weights for the ICR are dry.
The overall weight of the RO water plant of Table 8 takes advantage
of weight savings derived from the use of composite piping on the
low-pressure seawater side of the system. The largest volume and
weight savings derive from the compact stacks (see previous
discussion), which are about one third the size of those in the
baseline LM2500 system.
Table 9 compares the volumes and weights of the three alternative
propulsion plants under study here. The ICR plant is slightly more
compact in size than the baseline LM2500 plant, whereas the SAGT
plant is about 30% more compact in size than the baseline. The ICR
plant is heavier than the baseline plant. However, for a ship
weight of 8000 tons, the difference between "light" and "full" load
is about 400 to 500 tons. Therefore, an incremental weight of 68
tons will exhibit no negative ship impact unless that weight, by
virtue of maldistribution, unduly shifts (e.g., elevates) the ship
center of gravity. The nine-ton increment in the SAGT plant is, in
fact, beneficially distributed relative to the ship center of
gravity because the elevated, high-moment weight in the stacks is
considerably reduced. Thus, for the SAGT plant, the 9-ton increase
in weight is expected to yield a neutral, if not benign, ship
impact.
TABLE 9 ______________________________________ Alternative system
volumes and weights. VOLUME WEIGHT SYSTEM ft.sup.3 (m.sup.3) RATIO
(lb (m.t)) RATIO ______________________________________ LM2500
39140 1 906000 1.0 (1108) (411) ICR 38345 0.98 1056000 1.17 (1086)
(479) SAGT 26874 0.69 925320 1.02 (761) (420)
______________________________________
The significant reduction in overall ship volume suggests that the
compactness of the SAGT plant is likely to have a positive ship
impact on a DDG destroyer. This may be demonstrated by showing that
the SAGT plant may be laid out in traditional DDG spaces without
displacement of critical machinery systems.
FIGS. 8(a) and 8(b) illustrate the physical space of the aft engine
room of a conventional LM2500 plant of a DDG-51 destroyer. The SAGT
propulsion plant is approximately laid out in spaces allotted for
the existing system. Selected scaled layouts include a plan view of
the second platform, as shown in FIG. 8(a), and an overall side
elevation of three decks, as shown in FIG. 8(b). To accommodate the
ROD module skids on the second platform (FIG. 8(a)), the lube-oil
storage and settling tanks, as well as their associated machinery,
must be relocated to the first platform. The existing deck
perimeter was extended toward starboard to within a reasonable
standoff distance from the propulsion shaft and reduction gear.
This provided sufficient space for other machinery that must be
accommodated on this level, i.e., the intercooler, SWH, and the
seawater pump.
In the SAGT-engine application, the deck standoff distance from the
reduction gear was markedly reduced from that in the existing
layout. The module skids were arranged in a manner which would
allow sharing of the element pull space that is allocated between
adjacent skids. Preferably, a minimum peripheral clearance of at
least 18 inches around all machinery is maintained, but in a few
noncritical situations, clearance can be reduced to 12-15 inches.
As in the baseline layout, athwartship shifting of the uptake
centerline begins above the 01 level, which is the point where the
HRSG nozzle, shown in FIG. 8(b), terminates; i.e., the nozzle and
turbine-exhaust centerlines are in the same longitudinal plane.
Sufficient vertical height was allocated for the exhaust diffuser
(below the HRSG) to ensure that flow distortion and its associated
pressure loss will be minimal.
On the main deck, the space freed up by removal of the intake and
uptake was effectively utilized in locating the remaining
components of the SAGT plant. The layouts signify that the allotted
spaces permit the SAGT plant to be installed with little if any
negative ship impact on important machinery suites.
Further, the present inventors have found that the SAGT system is
competitive with the existing power plants on a first-cost
basis.
The SAGT engine, and in particular, the new SAGT engine with a dual
(i.e., low- and high-) pressure combustor, are unique in that they
simultaneously yield efficiency, compactness and affordability in a
single package.
While propulsion power for a destroyer type vessel has been
described above, development of the SAGT concept is applicable to
main propulsion, ships-service power, pulse-power devices and
combinations thereof, and land-based operations.
According to the invention, the new SAGT engine may be constructed
from off the-shelf hardware and is relatively inexpensive to
manufacture. SAGT engines without low-pressure, reheat combustors
yield a 21.5% decrease in fuel consumption over the existing LM2500
simple-cycle engines used for Navy ships, whereas estimates based
on the use of low-pressure reheat combustors indicate more than a
23% decrease in fuel consumption relative to the same baseline. The
efficiency of the new SAGT is equal to or greater than that of
combined steam and gas turbine (STAG) systems. This efficiency
reduces the life-cycle cost of the system.
Further, the SAGT-engine power plant is 30% more compact than the
alternative baseline simple-cycle power plant. Thus, the SAGT plant
has a smaller footprint in comparison to the conventional engines.
As a consequence, it has little or no negative impact upon other
shipboard machinery systems. Further, the simultaneous combination
of fuel efficiency, compactness, and competitive first cost makes
for more affordability and low life-cycle cost. Another potential
of the SAGT concept is the enhanced engine stability under load
variations. This arises from the additional degrees of freedom
inherent in steam augmentation, and low-pressure combustion.
Further, the simple-cycle LM2500 engines and the STAG engine
systems found in commercial service produce more nitrogen-oxide
effluents than do the SAGT engines. Additionally, the LM2500
baseline engines are less efficient than SAGT or STAG engines.
Typical efficiencies of 36% are observed for an LM2500 versus 42.5%
for SAGT or STAG engines (for turbine inlets temperatures of 2200
F). In space-limited ship systems, the alternatives require more
volume, and present more negative ship impact.
While the invention has been described in terms of specific
embodiments, those skilled in the art will recognize that the
invention can be practiced with modification within the spirit and
scope of the appended claims.
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